TITLE: GCN CIRCULAR NUMBER: 29636 SUBJECT: GRB 210306A: Swift/UVOT Detection DATE: 21/03/09 14:05:28 GMT FROM: Kira Simpson at PSU GRB 210306A: Swift/UVOT Detection K. K. Simpson (PSU) and V. D'Elia (SSDC) report on behalf of the Swift/UVOT team: The Swift/UVOT began settled observations of the field of GRB 210306A 85 s after the BAT trigger (D'Elia et al., GCN Circ. 29597). A source consistent with the XRT position (D'Elia et al. GCN Circ. 29597) is detected in the initial UVOT exposures. The preliminary UVOT position is: RA (J2000) = 08:39:49.98 = 129.95824 (deg.) Dec (J2000) = +60:12:19.2 = 60.20533 (deg.) with an estimated uncertainty of 0.42 arc sec. (radius, 90% confidence). Preliminary detections using the UVOT photometric system (Breeveld et al. 2011, AIP Conf. Proc. 1358, 373) for the early exposures are: Filter T_start(s) T_stop(s) Exp(s) Mag white 85 235 147 16.23 +/- 0.03 v 628 648 20 17.42 +/- 0.24 b 553 573 20 17.32 +/- 0.13 u 297 547 246 16.86 +/- 0.04 The magnitudes in the table are not corrected for the Galactic extinction due to the reddening of E(B-V) = 0.052 in the direction of the burst (Schlegel et al. 1998).